This invention relates to a method of estimating the weight of a vehicle seat occupant for purposes of allowing or suppressing deployment of inflatable restraints, and more particularly to a method of compensating the estimated occupant weight based on weight applied to the vehicle floor forward of the seat.
Vehicle seat occupant weight estimation systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of characterizing the occupant for purposes of determining whether to allow or suppress deployment of the restraints. Typically, deployment is allowed for a child or small adult occupant, suppressed or reduced in force for a small child, and suppressed when an infant seat is detected. See, for example, the U.S. Pat. Nos. 5987370, 6101436, 6138067 and 6246936, which are assigned to the assignee of the present invention and incorporated herein by reference. The systems described in such patents measure the fluid pressure in a seat cushion bladder as an indication of occupant weight, and compare the indicated weight to one or more thresholds to appropriately characterize the occupant. Alternatively, the seat occupant weight can be estimated with a different type of sensor, such as a seat cushion pad having a number of cells that vary in resistance or capacitance due to the presence of an occupant.
Regardless of how the occupant seat weight is detected, under-estimation of the occupant weight can occur in cases where a significant portion of the occupant""s weight is off-loaded to the vehicle floor forward of the seat. The degree of such off-loading will of course vary with the posture of the occupant, the seat height and inclination, and so on, and clinical evaluation of this phenomenon reveals that the off-loaded weight is typically about 30% of the full occupant weight. While it would be desirable to somehow compensate the estimated occupant weight for weight applied to the floor forward of the seat, it is not readily apparent how such compensation could be achieved out since the occupant may place various objects such as sports equipment or a heavy purse or grocery bag on the floor, and such objects are not indicative of occupant weight. Accordingly, what is needed is a method of detecting weight applied to the floor forward of a vehicle seat, and discerning what portion of the detected floor weight is attributable to the occupant for purposes of suitably compensating an estimated weight of the occupant.
The present invention is directed to an improved vehicle seat occupant weight estimation method that detects weight applied to both the seat cushion and the floor forward of the seat, and that increases the measured seat weight of the occupant to account for occupant weight off-loaded to the floor. In the preferred embodiment, fluid-filled bladders are arranged to detect occupant seat weight and the weight applied to the vehicle floor forward of the seat. Upon opening of a vehicle door or an off-to-on transition of the vehicle ignition switch, the seat and floor weight sensors are monitored to detect the presence of an occupant. When the seat becomes occupied, or whenever there is a large change in the measured seat weight, the seat and floor weight are recorded, the occupant weight is estimated according to the recorded seat weight, and the inflatable restraints are allowed or suppressed based on the estimated occupant weight. When a sustained shift in occupant weight is detected, the estimated occupant weight is increased in proportion to the amount of weight shifting, but is limited to a maximum value based on the detected floor and seat weights.